Many of the groups, which include Western Watersheds Project, WildEarth Guardians and the Center for Biological Diversity, filed a similar petition in Idaho in March. Wildlife Services, an arm of the U.S. Department of Agriculture, decided to remove all M-44s from private, state and federal land in Idaho.

“We’re not at war with native wildlife, and it is irresponsible to allow poison landmines to be sown anywhere in Wyoming,” said Erik Molvar, executive director of Western Watersheds Project. “Wildlife Services got rid of M-44s in Idaho, and they should do the same in Wyoming before more pets, and even people, get hurt or killed.”

Trappers in Wyoming began using M-44s in 1975. The traps kill by injecting sodium cyanide powder into an animal’s mouth that releases hydrogen cyanide gas when mixed with saliva. Because the poison is metabolized instantly, M-44s are seen as a less hazardous way to kill predators than poisons like the now-banned 1080, which stays in carcasses and eviscerated populations of predators such as eagles and wolverines.

In the winter, the USDA Wildlife Services might have about 250 M-44s on the landscape in Wyoming, Mike Foster, state director of Wildlife Services, told the Star-Tribune in April.